Within the field of packaging food products, and in particular packaging such products under aseptic conditions use is often made of sterilized packaging containers, such as Tetra Brik Aseptic (registered trademark). Tetra Brik Aseptic, as well as similar packages, may be manufactured by forming and scaling a strip-rolled packaging material. The packaging material comprises a layer of fibrous material, such as paper, sandwiched between two or more layers of thermoplastic, such as polyethylene. The side of the packaging material to be contacted by product may also comprise a barrier material layer, such as an aluminum layer, which in turn is covered by a layer of thermoplastic material.
In a typical packaging process the packaging material is sterilized, whereafter the two longitudinal edges of the packaging material are joined such as to form a continuous tube. The tube of packaging material is filled with product, usually sterilized product, after which the tube is provided with transversal seals such as to form pillow-shaped packages that may be severed from the continuous tube and folded into individual packaging containers. The present invention has an immediate application in the transversal sealing of the tube, yet it may be used for transfer of power for all types of induction heating sealing systems, or all types of sealing systems in general.
In the context of transversal sealing packaging machines are known comprising two opposing chain conveyors, each defining an endless path. The two chain conveyors comprise opposing sealing jaws and counter-jaws, respectively, such that the tube of packaging material may be clamped between a sealing jaw and a counter jaw and exposed to a sealing action in order to form packaging containers. There are a number of options available for the sealing action, such as direct heating of the packaging material, and inductive heating of the packaging material, both well-known within the present field.
In both of these examples power, or current, has to be transferred to the sealing jaw, i.e. transferred from a stationary source of energy to a moveable device. This transfer of energy may be effected in various ways, e.g. in a first method, the jaws fitted with the heating means are also fitted with brushes preferably made of carbon, and which, along a predetermined portion of their travel, slide along respective copper power bars fixed to the packaging machine frame.
Though functional and efficient there is always room for improvement e.g. in terms of operational lifetime of the device. Packaging units incorporating this type of power transfer systems are disclosed in EP-A-0 887 265 and in EP-A-0 887 270, by the present applicant, and are considered to be well-known to the skilled person.
A second method has been developed wherein electric energy is transferred from the stationary energy source to the movable device by electromagnetic induction. One example of this method applied to chain-type packaging machines is described in Patent Application WO 00/64662.